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3축 마이크로 공작기계용 자기예압 공기베어링 스테이지의 정, 동적 특성
노승국,Kornel F. Ehmann,Yoon, Hyung-Suk,박종권 한국공작기계학회 2005 한국공작기계학회 춘계학술대회논문집 Vol.2005 No.-
In this paper, the static and dynamic stiffness of the air bearing stage for micro-micro machine tool are examined experimentally. For stiffness and precision concerns, air bearing stages are adapted for 3-axis micro-milling machine which is size of 200x200 mm². The air bearings in the stage are preloaded by permanent magnets to achieve desired bearing clearance and stiffness for vertical direction. As the stiffness of the air bearing is primary interests, static stiffness test were performed on XY stage in Z direction and Z column in Y direction. Dynamic test were performed on XY stage and Z column, respectively. Both static and dynamic tests were performed in different air pressure conditions. The vertical stiffness of XY stage is about 9N/μm where Y stiffness of Z column is much smaller as 1N/μm because of the large moment generated by Y force on the column.
Development of a two-frequency, elliptical-vibration texturing device for surface texturing
쿠르니아완렌디,고태조,Li Chang Ping,띠뚜말라이쿠마란,Gandjar Kiswanto,Ping Guo,Kornel F. Ehmann 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.7
This study presents the design of a Two-frequency, elliptical-vibration texturing (TFEVT) device. The device was designed to be used in a surface texturing process, and its functionality is based on a combination of ultrasonic (> 20 kHz) and low vibration frequencies (< 100 Hz). The device consists of two parts: The Ultrasonic elliptical motion transducer (UEMT) and the Low frequency displacement amplifier (LFDA). A modal analysis simulation and dynamic experiments were conducted to investigate the dynamic characteristics of the device. The modal simulation was carried out using finite element analysis and the dynamic experiment was evaluated using Frequency response function (FRF) analysis. The working principle of the UEMT is based on a resonance transducer, and the angle between the two Langevin transducers was set as 90 o . The UEMT has two vibration modes, symmetric and asymmetric, and according to experimental data, its working frequency is 24 kHz at the 6 th resonance vibration mode when a Polycrystalline diamond (PCD) tool is attached. The UEMT is able to generate an elliptical locus that has a vertical amplitude of 1.4 µm and a horizontal amplitude of 0.6 µm, under a phase-shift of 90 o . The design of the LFDA is based on a double parallel four-bar flexure hinge, and the displacement output ratio is set to 5. The working principle of the LFDA is based on a non-resonance transducer. The working frequency of the LFDA is below its first of natural frequencies (≈1060 Hz), and it is able to generate sinusoidal motion with a maximum peak-to-peak amplitude of 9 µm. Finally, to investigate the feasibility of the TFEVT device for use in a surface texturing process, several micro-groove cutting tests were performed on an AISI 1045 alloy steel.
Error modeling for sensitivity analysis and calibration of the tri-pyramid parallel robot
Lee, Sungcheul,Zeng, Qiang,Ehmann, Kornel F. Springer-Verlag 2017 INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TE Vol.93 No.1
<P>Developments in machine tooling technology are driven by a demand for high-precision machining of various materials. However, high-precision machining using a kinematic model with nominal values is associated with inaccuracy as the machine errors are not accounted for. Therefore, it is important to precisely determine the machine error factors to produce an accurate error model. Complex models that use iterative calculation in the calibration process are time-consuming and resource-intensive. In this paper, a simplified error model was applied to a translational parallel tri-pyramid robot with three degrees of freedom (DOF). The sources of kinematic error were joint errors, kinematic parameter errors, and actuator control errors; 90 errors were identified in total. The full error model was defined using a linearized homogeneous transformation matrix (HTM) and the Denevit-Hartenberg (DH) parameters. The 27 dominant error sources affecting the accuracy of the platform position were selected by a sensitivity analysis method. After the error reduction model based on these sources was established, the calibration was performed by simulation. The calibration simulation results suggest that the model accuracy could be improved from 0.85 to 0.26 mm.</P>